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kenryan
Joined: 20 Oct 2009
Posts: 424
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 Posted: Mon Dec 11, 2017 1:56 pm Post subject: diode vs snapjack |
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Which is better for use on relays, the "standard" diode or the "snapjack" (bi-directional zener transient voltage suppressor)?
Ken
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user9253
Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan
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| Posted: Mon Dec 11, 2017 4:29 pm Post subject: Re: diode vs snapjack |
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Whichever is less expensive and easiest to install. A few years ago there was a "heated discussion" between two very knowledgeable people on this forum. I listened to both sides and do not think it matters.
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Joe Gores |
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nuckolls.bob(at)aeroelect
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| Posted: Tue Dec 12, 2017 8:58 am Post subject: diode vs snapjack |
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At 03:54 PM 12/11/2017, you wrote:
| Quote: | Which is better for use on relays, the "standard" diode or the "snapjack" (bi-directional zener transient voltage suppressor)?
Ken
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Diodes are fine . . . there were some lengthy discussions
on the 'advantages' of voltage compliant spike suppression
about 10 years. A great deal of homage was paid
to a document published by Tyco no less wherein the author
claimed that hard clamping of the coil spike by diode
slowed contact spreading velocity and increased wear and
tear on the relay.
Yes, the diode causes a DELAY in the first motion
of the opening contacts . . . but before the contacts
start to move, an AIR GAP is introduced into the
magnetic circuit that generates the closing force.
This air gap has many times more effect on contact
spreading velocity than does the decay rate of current
in the coil.
The Tyco author laid all his eggs in the magnetic
force decay due to current in the coil and totally
ignored the air gap effects. A simple workbench
experiment would have illuminated his attribution
error for cause/effect.
I spent a few years sifting the sands of relay performance
and failures at Beech. Many of the young bucks wearing the
boots of their predecessors as engineering reps for relay
and contactor manufacturers were glaringly deficient in
mentorship by those predecessors . . .
Bob . . .
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kenryan
Joined: 20 Oct 2009
Posts: 424
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| Posted: Tue Dec 12, 2017 9:38 am Post subject: diode vs snapjack |
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Thanks Bob. Is there any disadvantage to the snapjacks?
On Tue, Dec 12, 2017 at 7:57 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 03:54 PM 12/11/2017, you wrote:
| Quote: | Which is better for use on relays, the "standard" diode or the "snapjack" (bi-directional zener transient voltage suppressor)?
Ken
|
Diodes are fine . . . there were some lengthy discussions
on the 'advantages' of voltage compliant spike suppression
about 10 years. A great deal of homage was paid
to a document published by Tyco no less wherein the author
claimed that hard clamping of the coil spike by diode
slowed contact spreading velocity and increased wear and
tear on the relay.
Yes, the diode causes a DELAY in the first motion
of the opening contacts . . . but before the contacts
start to move, an AIR GAP is introduced into the
magnetic circuit that generates the closing force.
This air gap has many times more effect on contact
spreading velocity than does the decay rate of current
in the coil.
The Tyco author laid all his eggs in the magnetic
force decay due to current in the coil and totally
ignored the air gap effects. A simple workbench
experiment would have illuminated his attribution
error for cause/effect.
I spent a few years sifting the sands of relay performance
and failures at Beech. Many of the young bucks wearing the
boots of their predecessors as engineering reps for relay
and contactor manufacturers were glaringly deficient in
mentorship by those predecessors . . .
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Tue Dec 12, 2017 10:09 am Post subject: diode vs snapjack |
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At 11:37 AM 12/12/2017, you wrote:
| Quote: | | Thanks Bob. Is there any disadvantage to the snapjacks? |
costs more
Bob . . .
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